Selective activation of cat primary auditory cortex by way of direct intraneural auditory nerve stimulation

OBJECTIVES/HYPOTHESIS: Although cochlear implants have been successfully used by many individuals with profound hearing impairment, limitations still remain with this approach to hearing restoration, including poor stimulation selectivity because of cross-talk between electrodes and poor low-frequency percepts. These limitations may be mitigated by direct intraneural stimulation of the auditory nerve by way of an array of penetrating microelectrodes. Such an approach should provide focal stimulation and selective activation of the nerve fibers, thereby minimizing cross-talk among implanted stimulating electrodes and evoking narrow-band frequency percepts. STUDY DESIGN: We investigated the activation of primary auditory cortex evoked by such direct intraneural electrical stimulation of the auditory nerve. METHODS: We implanted 11 penetrating microelectrodes in the cat auditory nerve, simulated the nerve by way of these electrodes, and recorded the evoked neuronal activity patterns in cat primary auditory cortex. We compared these activation patterns with acoustically evoked cortical activity patterns obtained in a different animal. RESULTS: Our results showed that direct stimulation of the auditory nerve evoked localized activity patterns in primary auditory cortex similar in spatial extent to those evoked by acoustic stimulation and that the extent of cortical activation by both acoustic and electrical stimuli was graded with stimulus intensity. These results suggest that the implanted electrodes can excite independent and small populations of nerve fibers. CONCLUSION: This study demonstrates the functional feasibility of direct intraneural auditory nerve stimulation with an array of penetrating microelectrodes and that such an approach could form the foundation for an auditory prosthesis with improved frequency coding.     

Imaging of electrode position in relation to electrode functioning after cochlear implantation

This study assessed the electrode position in cochlear implant patients and evaluated the extent to which the electrode position is determinative in the electrophysiological functioning of the cochlear implant system. Five consecutively implanted adult patients received a multichannel cochlear implant. In all patients, the electrical impedance and the electrically evoked compound action potentials were recorded immediately after implantation. Multislice computer tomography was performed 6 weeks postoperatively before switch-on of the cochlear implant. The electrode position relative to the modiolus was assessed and correlated to the electrophysiological measurements. All electrodes were fully inserted; this was confirmed by computer tomography. The individual electrode distance toward the modiolus could be most precisely analyzed for the basal part of the electrode array. It was thus decided to study the data of electrodes one, four, and seven. No correlation was found between electrical impedance and electrode distance. A significant correlation was found between electrode distance and the electrically evoked compound action potentials, with a 96% probability using Kendall’s rank correlation. We conclude that the electrode–modiolus distance is of importance to the stimulation of auditory nerve fibers. Future developments in imaging will further improve and refine our insight in the relation between electrode positioning.     

Development of a novel eighth-nerve intraneural auditory neuroprosthesis

OBJECTIVES/HYPOTHESIS: Cochlear nerve stimulation using a linear array of electrodes, the cochlear implant, has become an accepted treatment for profound deafness. Major limitations of this technology are high threshold of stimulation, poor performance in a noisy background, cross-talk between electrodes, unsatisfactory channel selectivity, and variable reconstruction of frequency space. A novel auditory neuroprosthesis is proposed that is expected to overcome these problems by implanting an array of three-dimensional microelectrodes, the Utah Electrode Array, directly into the cochlear nerve. STUDY DESIGN: We have conducted acute, extending for up to 12 hours and semichronic, extending for up to 52 hours, electrophysiological experiments, radiologic and histologic studies in 12 cats. METHODS: The electrically evoked auditory brainstem response was used as a means to characterize the threshold, dynamic range, and stability of cochlear nerve stimulation through the implanted Utah Electrode Array neuroprosthesis. Plain film, computed tomographic, and histological studies were conducted to determine the result of the implant. RESULTS: The electrically evoked auditory brainstem response thresholds were approximately one to two orders of magnitude lower than those evoked with conventional cochlear implants. We were able to close the cochleostomy, bring the cat into normal anatomical position, and obtain stable electrically evoked auditory brainstem responses for up to 52 hours. Plain film and computed tomographic studies indicated that the Utah Electrode Array neuroprosthesis was in the intended position in the nerve. Histological studies did not reveal hemorrhage or significant damage to the nerve. CONCLUSION: Because the presented stimulation paradigm appears to significantly mitigate some of the problems of conventional cochlear implants, it may offer a new therapeutic approach to profound deafness.     

Intracochlear potential distribution with intracochlear and extracochlear electrical stimulation in humans

Intracochlear potential distributions were measured from subjects implanted with the Ineraid multichannel cochlear implant. The electrode array provided direct accessibility for obtaining measurements. Different modes of stimulation were used. The findings with intracochlear monopolar stimulation seem to confirm that significant low-resistance pathways, in which currents can flow into or out of the cochlea, are located in the basal turn. The results with extracochlear stimulation only show small intracochlear potential gradients. This finding suggests that no substantial currents flow along the auditory nerve fibers when extracochlear stimulation is used. These results concur with the electrically evoked auditory brain stem responses, in that intracochlear stimulation consistently elicited auditory brain stem responses, whereas responses elicited at or near the round window by extracochlear stimulation were weak or absent.     

A technique for implantation of a 3-dimensional penetrating electrode array in the modiolar nerve of cats and humans

BACKGROUND: We believe that direct intraneural stimulation of the modiolar nerve using an array of electrodes will have lower thresholds, offer greater frequency selectivity and more stimulation sites, and have a greater frequency representation than conventional cochlear implants. OBJECTIVES: To describe a potential auditory prosthesis based on electrical stimulation of the modiolar cochlear nerve and to report the development of a surgical approach in human and animal models. DESIGN: Cadaveric human and animal studies conducted in temporal bones indicated that an array of penetrating microelectrodes could be implanted in the modiolar nerve. Cat studies using anesthesia were performed to develop the surgical procedure in an animal model. Nerve viability was assessed by measurement of electrically evoked auditory brainstem responses at different stages of the surgery. SUBJECTS: Two fresh cadaveric human temporal bones, 3 cat cadavers, 1 pig cadaver, and 6 anesthetized cats were used in the experiments. RESULTS: We were able to implant arrays containing 20 microelectrodes in the human modiolar nerve after exposure by a modified extended facial recess approach. In animals, the modiolar nerve was accessed by the transbulla and the middle fossa approach. The cat was chosen as the appropriate animal model, and the transbulla approach was selected. The round window was exposed by ventral access to the bulla and after cochleostomy; drilling the modiolar bone exposed the modiolar nerve. The mean +/- SD diameter of the exposed nerve in cats was 1.64 +/- 0.07 mm (n = 9), and the mean +/- SD exposed length was 2.50 +/- 0.11 mm (n = 9); this is adequate to accommodate 20 microelectrodes. The electrically evoked auditory brainstem responses indicated nerve survival during and after the surgery. CONCLUSIONS: The surgical technique allows implantation of up to 20 microelectrodes in the cat and human modiolar nerve. The nerve survives the surgical procedure. This work enables studies in the electrophysiological properties and consequences of long-term implantation.     

Auditory Prosthesis with a Penetrating Nerve Array

Contemporary auditory prostheses (“cochlear implants”) employ arrays of stimulating electrodes implanted in the scala tympani of the cochlea. Such arrays have been implanted in some 100,000 profoundly or severely deaf people worldwide and arguably are the most successful of present-day neural prostheses. Nevertheless, most implant users show poor understanding of speech in noisy backgrounds, poor pitch recognition, and poor spatial hearing, even when using bilateral implants. Many of these limitations can be attributed to the remote location of stimulating electrodes relative to excitable cochlear neural elements. That is, a scala tympani electrode array lies within a bony compartment filled with electrically conductive fluid. Moreover, scala tympani arrays typically do not extend to the apical turn of the cochlea in which low frequencies are represented. In the present study, we have tested in an animal model an alternative to the conventional cochlear implant: a multielectrode array implanted directly into the auditory nerve. We monitored the specificity of stimulation of the auditory pathway by recording extracellular unit activity at 32 sites along the tonotopic axis of the inferior colliculus. The results demonstrate the activation of specific auditory nerve populations throughout essentially the entire frequency range that is represented by characteristic frequencies in the inferior colliculus. Compared to conventional scala tympani stimulation, thresholds for neural excitation are as much as 50-fold lower and interference between electrodes stimulated simultaneously is markedly reduced. The results suggest that if an intraneural stimulating array were incorporated into an auditory prosthesis system for humans, it could offer substantial improvement in hearing replacement compared to contemporary cochlear implants.     

Chronic intracochlear electrical stimulation in the neonatally deafened cat. I: Expansion of central representation

Intracochlear electrical stimulation via cochlear prostheses has been employed as a means of providing some hearing to deaf children. Since chronically restricted stimuli are known to have profound effects on central nervous system development, it is important to examine the effects of chronic intracochlear electrical stimulation in a neonatally deafened animal model. In this study neonatally deafened cats were implanted with a scala tympani electrode consisting of two pairs of electrodes. Chronic electrical stimulation was delivered using one electrode pair and consisted of charge-balanced biphasic pulses (200 μs/phase, 30 pps) at 2 dB above the electrically evoked auditory brain stem response (EABR) threshold for 4 h/day or at 6 dB 1 h/day, 5 days/week, for up to 3 months. The second electrode pair was unstimulated and served as an internal control. Following chronic stimulation, acute mapping experiments were performed in the central nucleus of the inferior colliculus (ICC) using single unit and multi-unit recording techniques and activating each electrode pair separately.In addition to these chronically stimulated animals, 2 other groups of experimental animals were studied: A normal group consisting of prior normal adult cats that were acutely implanted; and an unstimulated control group consisting of neonatally deafened adult cats that were either acutely implanted or implanted at 8–10 weeks of age but not chronically stimulated.

Among the major findings of this study are: Electrical stimulation of the intracochlear bipolar electrode consistently produces activation of a reproducibly limited sector of the ICC. The location of this activated sector was found to be consistent with the known cochleotopic organization of the ICC and the intracochlear location of the stimulating electrodes. No major differences in the spatial representation of activated electrodes were found between prior normal cats and neonatally deafened unstimulated cats. The locations, shapes and widths of these spatial representations were virtually indistinguishable indicating that ICC cochleotopic organizations were equivalent in these two experimental groups. In contrast, the ICC representation of chronically stimulated electrode pairs were found to be significantly different. The average area activated by chronically stimulated electrode pairs at 6 dB above minimum threshold was approximately twice that of unstimulated deafened animals and prior normal animals; and it was larger, but not significantly so, than the average of the unstimulated electrode pair in the same experimental group.

These results indicate that: 1) One of the fundamental features of the central auditory organization, the orderly topographic representation of cochlear place, is unaltered (at least to the level of the midbrain) by the lack of normal acoustic input during development. 2) Electrical stimulation of very limited duration and intensity delivered to a restricted sector of the cochlear spiral can expand the central representation of that sector and alter cochleotopic representations in the auditory CNS.     

Activity-dependent developmental plasticity of the auditory brain stem in children who use cochlear implants

OBJECTIVES: 1) To determine if a period of early auditory deprivation influences neural activity patterns as revealed by human auditory brain stem potentials evoked by electrical stimulation from a cochlear implant. 2) To examine the potential for plasticity in the human auditory brain stem. Specifically, we asked if electrically evoked auditory potentials from the auditory nerve and brain stem in children show evidence of development as a result of implant use. 3) To assess whether a sensitive or critical period exists in auditory brain stem development. Specifically, is there an age of implantation after which there are no longer developmental changes in auditory brain stem activity as revealed by electrically evoked potentials? DESIGN: The electrically evoked compound potential of the auditory nerve (ECAP) and the electrically evoked auditory brain stem response (EABR) were recorded repeatedly during the first year of implant use in each of 50 children. The children all had pre- or peri-lingual onset of severe to profound sensorineural hearing loss and received their implants at ages ranging from 12 mo to 17 yr. All children received Nucleus cochlear implant devices. All children were in therapy and in school programs that emphasized listening and required the children to wear their implants consistently. RESULTS: Initial stimulation from the cochlear implant evoked clear responses from the auditory nerve and auditory brain stem in most children. There was no correlation between minimum latency, maximum amplitude, or slope of amplitude growth of initial responses with age at implantation for ECAP eN1, EABR eIII and eV components (p > 0.05). During the first year of implant use, minimum latency of these waves significantly decreased (p < 0.01, p < 0.0001, p < 0.0001, respectively). Neural conduction time, measured using the interwave latency of ECAP eN1-EABR eIII for lower brain stem and EABR eIII-eV for upper brain stem, decreased during the period of 6 to 12 mo of cochlear implant use (p < 0.01 (lower), p < 0.0001(upper)). The ECAP wave eN1 and the EABR wave eV showed significant increases in amplitude during time of implant use (p < 0.05 and p < 0.01, respectively). There were no correlations between the rate of interwave latency decrease and the rate of amplitude increases and the age at which children underwent implantation (p < 0.05). CONCLUSIONS: Activity in the auditory pathways to the level of the midbrain can be evoked by acute stimulation from a cochlear implant. EABR measures are not influenced by any period of auditory deprivation. Auditory development proceeds once the implant is activated and involves improvements in neural conduction velocity and neural synchrony. Underlying mechanisms likely include improvements in synaptic efficacy and possibly increased myelination. The developmental plasticity that we have shown in the human auditory brain stem does not appear from EABR data to be limited by a critical period during childhood.     

Intraneural stimulation for auditory prosthesis: modiolar trunk and intracranial stimulation sites

We have demonstrated recently in an animal model that stimulation with a penetrating auditory nerve electrode array is a feasible means of activating the ascending auditory pathway for auditory prosthesis. Compared to a conventional intrascalar cochlear implant, intraneural stimulation provides access to fibers serving a broader frequency range, activation of more tonotopically restricted fiber populations, lower thresholds, and reduced interference between simultaneously stimulated channels. The spread of excitation by a single intraneural electrode is broader than that by an acoustic tone but narrower than that by a cochlear-implant electrode. In the present study, we compare in an animal model two sites of intraneural stimulation: the modiolar trunk of the nerve accessed using a transcochlear approach and the intracranial portion of the nerve accessed using a posterior fossa approach. The two stimulation sites offer very similar thresholds, spread of activation, and dynamic ranges. The intracranial site differed in that there was greater between-animal variation in tonotopic patterns. We discuss the implications of these results for possible improvements in hearing prosthesis for human subjects.     

Electrically evoked potentials in cochlear implant subjects

A series of experiments was performed to study electrically evoked potentials as indicators of subject response to cochlear implantation. 1. Brain stem evoked responses to electrical stimulation were compared to those obtained by acoustic stimulation in guinea pigs. The response pattern was similar and was independent of the site of placement of the stimulus electrode (cochlear base or apex) or of the extracochlear ground electrode (eustachian tube or temporalis muscle) when evoked electrically. 2. Electrically evoked middle latency responses were recorded and compared to subjective behavioral thresholds in patients who had received a single channel cochlear implant (House-Urban). The behavioral responses to the same stimuli were similar. 3. Electrically evoked auditory brain stem responses were studied in single channel cochlear implant subjects (3M/House). When evoked electrically, potential latencies were shorter and interpeak intervals narrower than acoustically evoked potentials.     

Electrically evoked auditory brainstem response monitoring of auditory brainstem implant integrity during facial nerve tumor surgery.

Evoked potentials identified as electrically evoked auditory brainstem responses (EABRs) have been recorded from a patient in response to electrical stimulation of the cochlear nucleus via an auditory brainstem implant. Recording such EABRs during surgery for removal of an ipsilateral facial nerve tumor provided a means to monitor the integrity of the implant. The presence of stable EABRs similar to those obtained before surgery indicated that the lead wires had not been severed and that the implanted electrodes had not been dislodged. EABR recording may also be useful for assisting with positioning the stimulating electrodes during initial implantation surgery, by verifying that stimulation can activate the auditory system.     

Auditory neuropathy in systemic sclerosis: a speech perception and evoked potential study before and after cochlear implantation

We report the results of speech perception and electrophysiological evaluation of the auditory periphery performed before and after cochlear implantation in a 18-year-old girl with systemic sclerosis (SS) who presented the clinical picture of auditory neuropathy. Transtympanic electrocochleography (ECochG) in response to 0.1 ms clicks was recorded 1 month before cochlear implantation on both sides while the electrically evoked neural response was obtained intraoperatively in the right ear through cochlear implant stimulation. The ECochG recordings revealed the presence of the cochlear microphonic with normal amplitude and threshold on both sides. A compound action potential was only detected in the left ear at high stimulation intensity, while the electrically evoked neural response was clearly identifiable at all the recording sites during neural response telemetry. Standardized speech perception tests were performed 1 month before cochlear implantation and several times after cochlear implant connection. Speech perception scores were close to chance before cochlear implantation while they showed a remarkable improvement thereafter. The results of this study show that subjects affected by SS could present the clinical picture of auditory neuropathy which is possibly underlain by lesions involving the distal portion of auditory nerve fibers and/or synapses with inner hair cells. The restoration of synchronous neural discharge could be achieved by electrical stimulation through cochlear implant.     

Using Evoked Potentials to Match Interaural Electrode Pairs with Bilateral Cochlear Implants

Bilateral cochlear implantation seeks to restore the advantages of binaural hearing to the profoundly deaf by providing binaural cues normally important for accurate sound localization and speech reception in noise. Psychophysical observations suggest that a key issue for the implementation of a successful binaural prosthesis is the ability to match the cochlear positions of stimulation channels in each ear. We used a cat model of bilateral cochlear implants with eight-electrode arrays implanted in each cochlea to develop and test a noninvasive method based on evoked potentials for matching interaural electrodes. The arrays allowed the cochlear location of stimulation to be independently varied in each ear. The binaural interaction component (BIC) of the electrically evoked auditory brainstem response (EABR) was used as an assay of binaural processing. BIC amplitude peaked for interaural electrode pairs at the same relative cochlear position and dropped with increasing cochlear separation in either direction. To test the hypothesis that BIC amplitude peaks when electrodes from the two sides activate maximally overlapping neural populations, we measured multiunit neural activity along the tonotopic gradient of the inferior colliculus (IC) with 16-channel recording probes and determined the spatial pattern of IC activation for each stimulating electrode. We found that the interaural electrode pairings that produced the best aligned IC activation patterns were also those that yielded maximum BIC amplitude. These results suggest that EABR measurements may provide a method for assigning frequency–channel mappings in bilateral implant recipients, such as pediatric patients, for which psychophysical measures of pitch ranking or binaural fusion are unavailable.     

Brainstem responses to electrical stimulation of cochlea

We performed a brainstem evoked response (BSER) study to evaluate the extent to which electrical stimulation of the cochlea was conducted centrally by facial, vestibular, and cochlear nerves. Short-term experiments were performed in three monkeys: via a postauricular approach to the round window, a molded Silastic multielectrode prosthesis was placed in the scala tympani. The BSER was recorded to threshold and suprathreshold biphasic electrical pulses delivered to the implant electrodes. A middle cranial fossa dissection was then carried out, exposing the nerves of the internal auditory canal from above. Facial and vestibular neurotomy had no significant effect on BSER, while cochlear nerve section abolished the response. In one animal, blunt pressure on the cochlear nerve caused a reversible loss of electrically evoked BSER. Electrically evoked BSER probably depends on propagated impulses in the cochlear nerve.     

Electrode Interaction in Pediatric Cochlear Implant Subjects

Multielectrode cochlear implants rely on differential stimulation of the cochlear nerve for presenting the brain with the spectral and timing information required to understand speech. In implant patients, the degree of overlap among cochlear nerve fibers stimulated by the different electrodes constitutes the electrode interaction. Electrode interaction degrades the spectral resolution of the implant’s stimulus. We sought to define electrode interaction in a cohort of pediatric cochlear implant subjects as a function of both stimulus intensity and electrode location along the array. The 27 pediatric subjects that completed the study were implanted with either the Clarion Hi-Focus array with or without positioner, the Nucleus 24 Contour array, or the Nucleus 24 Straight array. All but two of the patients had congenital hearing loss, and none of the patients had meningitis prior to the onset of deafness. The cochlear nerve response was measured with the electrically evoked compound action potential (ECAP). A forward masking protocol was used such that a probe stimulus electrode remained fixed while a preceding masker was moved across the array. Electrode interaction was estimated by measuring the unmasked probe response minus the masked probe response. Three probe locations and three probe intensities were examined for each subject. At all probe locations, electrode interaction increased as probe intensity increased (p < 0.05). Interaction at the basal probe was less than that at either the middle or apical probe locations (p < 0.05), and significant correlation found between probe distance from the basal end of the array and electrode interaction (p < 0.001). These results demonstrate that in this cohort of pediatric subjects, electrode interaction depended on both stimulus intensity and probe location. Implications of these findings on future implant array design and current implant fitting strategies are discussed. The impact of electrode interaction on implant performance is yet to be elucidated.     

术中经蜗窗龛电刺激记录听性脑干反应方法的建立及初步应用

目的 建立人工耳蜗手术中经蜗窗龛电刺激记录听性脑干反应的方法.方法 应用自制铂铱合金球形电极作为刺激电极,改装的人工耳蜗植入体连接体外言语处理器作为电刺激仪及Bio-logic Navigator Pro诱发电位仪,对17例不同病因(包括听神经病2例、耳蜗骨化1例、内耳畸形5例、脑白质异常1例,原因不明8例),不同年龄的人工耳蜗植入患者在手术中进行测试.植入人工耳蜗装置前,将刺激电极放置在蜗窗龛内,用电荷平衡双相脉冲电流经蜗窗龛进行电刺激,记录电诱发听性脑干反应.结果 17例患者均记录到明确的电诱发听性脑干反应波形,Ⅲ波和Ⅴ波的潜伏期分别为(2.12±0.18)ms 和(4.18±0.19)ms,阈值为(220.00±16.04)CL.其中2例听神经病、5例内耳畸形、1例耳蜗骨化、1例脑白质异常患者均记录到分化良好的波形.结论 电诱发听性脑干反应是一项能够较准确地反映听觉传导通路功能完整性的客观神经电生理测试方法,对于判断人工耳蜗植入后患者能否获得听性反应,具有重要的应用价值.本研究方法的安全性符合要求,听性反应的引出率高,值得推广应用.     

Toward a battery of behavioral and objective measures to achieve optimal cochlear implant stimulation levels in children

OBJECTIVES: Children require audible and comfortable stimulation from their cochlear implants immediately after device activation. To accomplish this, a battery of objective measures may be needed that could include the electrically evoked stapedius reflex (ESR), compound action potential from the auditory nerve (ECAP), and/or auditory brain stem response (EABR). In the present study, the following specific research questions were asked: In children using cochlear implants, 1) Can the ECAP, EABR, and ESR be recorded at the time of cochlear implantation? 2) What is the feasibility of measuring the ECAP, EABR, and the ESR repeatedly without the use of sedation over the first year of implant use? 3) Do ECAP, EABR, and ESR thresholds or behavioral measures change over time? 4) What is the relation between ECAP, EABR, and ESR thresholds and behavioral measures of threshold and comfortably loud levels? DESIGN: In 68 children, ECAP, EABR, and ESR responses as well as behavioral measures of stimulation threshold and maximum stimulation were recorded at regular intervals over the first year of implant use. In each child, responses were recorded to electrical pulses provided by three different electrodes along the implanted array. Visual inspections of the stapedius reflex (V-ESR) evoked by activation of the same three electrodes at the time of surgery were performed in an additional 20 children. RESULTS: ECAP and EABR measures were obtained in more than 84% of electrodes tested and 89% of children tested both in the operating room at the time of implant surgery (OR) and after surgery in nonsedated children. ESRs were recorded by using immittance measures in more than 65% of electrodes tested and 67% of children tested by 3 mo of implant use, but this technique was less successful in the OR and during early stages of device use. V-ESRs and ECAP thresholds were higher in the OR than ESRs and ECAPs at postoperative recording times. EABR and ECAP thresholds did not significantly change over the first 6 and 12 mo of implant use, respectively, whereas ESR thresholds increased. Behavioral measures of threshold decreased over time, whereas maximum stimulation levels rose over time. Behavioral measures of threshold and loudness were highly correlated at all test times. ECAP, EABR, and behavioral measures were lower when evoked by an electrode at the apical end of the implanted array than by more basal electrodes. Behavioral thresholds could be predicted mainly by ECAP thresholds, whereas maximum stimulation levels could best be predicted by ESR thresholds; both were significantly affected by the age at implantation. CONCLUSIONS: A combination of nonbehavioral measures can aid in the determination of useful cochlear implant stimulation levels, particularly in young children and infants with limited auditory experience. These measures can be made in the operating room and can be repeated after surgery when needed. Correction factors to predict threshold stimulation levels should be based on ECAP thresholds or EABR thresholds if necessary. Correction factors should be made for at least one apical and mid-array electrode, should take into account the age of the child, and may have to be revised during the first year of implant use. Maximum stimulation levels may be best determined by using the ESR.     

Electrically evoked auditory brain stem responses for lateral and medial placement of the Clarion HiFocus electrode

OBJECTIVE: The purpose of this study was to compare the electrically evoked auditory brain stem response (EABR) for lateral and medial placement of the Clarion HiFocus cochlear implant electrode array via the electrode positioning system (EPS). DESIGN: Twenty-five adult and pediatric cochlear implant recipients participated in the study. Intraoperatively recorded EABRs were evoked by stimuli via three intracochlear electrodes representing apical, medial, and basal locations, and responses were elicited before and after positioner insertion. Evoked potential measures of wave V amplitude and threshold were examined for statistical significance using ANOVA for repeated measures and Chi-Square methods. RESULTS: For a given supra-threshold stimulus level, the increase in EABR wave V amplitude was significantly larger after EPS placement compared to before EPS placement for electrodes 1 (apical) and 13 (basal). Likewise, when the stimulus was decreased to obtain a minimal amplitude, the wave V threshold was significantly lower after EPS placement for electrodes 7 (medial) and 13. The number of measurements that showed decreased wave V threshold after EPS insertion was significantly dependent on intracochlear electrode location. CONCLUSIONS: Placement of the Clarion Electrode Positioning System following HiFocus electrode insertion resulted in a reduction in the electrical current required to activate the auditory system. The effect of the EPS was greatest for the basal location, demonstrated by lower wave V thresholds and a larger percentage increase in wave V amplitude. The EABR reflected electrophysiologic changes relative to lateral-to-medial changes in intracochlear electrode position due to the EPS.     

Nucleus24型人工耳蜗使用者电诱发听神经复合动作电位的测定

目的 :探讨电诱发听神经复合动作电位 (ECAP)的特点及在人工耳蜗临床中的应用价值和意义。方法 :应用NRT(neuralresponsetelemetry)软件 ,通过体外言语处理器和耳蜗内的植入电极系统 ,采用单极模式电极刺激和近场记录方法 ,对 37例NucleusCI2 4M装置使用者进行ECAP的记录。对其中 12例使用者做了行为测试。结果 :87.6 %的使用者记录到ECAP波形。分析了有行为阈值的 12例测试者的ECAP阈值和行为阈值的关系 ,二者之间存在显著的相关性。结论 :ECAP的检出率高且波形稳定可靠 ,在临床人工耳蜗装置的调试中可作为对行为测试的补充 ;对于年幼儿童和首次开机的患者的调试尤其重要     

Langzeitimplantation von Elektroden zur Elektrostimulation des N. acusticus im Tierexperiment

Summary Wire electrodes were implanted into the auditory nerve of four cats via the transoccipital approach. In the same session recording electrodes were fixed over the acoustic cortex. Evoked potentials were recorded after electric stimulation of the acoustic nerve and after acoustic stimulation of the contralateral ear. The level of the electrically induced responses was nearly constant for several months.Shape and latency of the potentials did not depend on the modality of the stimuli. The carefully investigated interaction of acoustic and electric stimulation showed no significant difference of both stimuli. In acoustically evoked potentials adaptation was more prominent, while in electrically evoked potentials higher amplitudes could be seen.